Shear Creep Studies of Narrow-Distribution Poly (as-isoprene)

Abstract

Shear creep measurements were made at temperatures between -68.6 and 98.0° on six narrow-distribution poly(cis-isoprene) samples with molecular weights of 57,600-1,120,000. The time-temperature reduction method was used for constructing master curves at a reference temperature of -30°. The curvss for two low molecular weight samples Mw = 57,600 and 103,000) showed deviations in the transition zone from those for other samples with higher molecular weights. Also, a corresponding effect of low molecular weight was observed on the shift factor aT. It was found that these effects were avoided by the use of a lower value for the reference temperature of the samples. The viscosity η and the steady-state compliance Je were determined by the extrapolation method of Ninomiya. Also the maximum relaxation time, rm, was evaluated by procedure X. It was found that η and τm varied as a power of the molecular weight, M3-45 and Je was independent of M. These results were in qualitative agreement with Hayashi's theory and also with Graessley's theory for entanglements. The entanglement spacing Me was about 3500 and was nearly independent of M determined from the inflection in the J(t) curve. © 1971, American Chemical Society. All rights reserved.